A siphon uses gravity and atmospheric pressure to move greywater outside. In order for this to work the landscape outside must be lower in elevation than the bottom of the tub. There are several ways to siphon greywater out of a bathtub. You can also read an article from Grist that shares several products on the market for siphoning.

1. Use a hand pump to start the siphon. Find a pump at a marine supply house, from Grainger, or possibly a hardware store.
2. Purchase a product made for this application. Siphon Aid is one.
3. Start the siphon with the bathtub faucet. Here’s how. Get a hose or tube long enough to run from the tub, out an open window/door, and down to the landscape. Put one end of the hose on the faucet, cup your hand around it to force water from the faucet into the hose. Once the hose is filled with water drop it into the tub and the siphon effect will pull water from the tub outside. The product Siphon Aid fits snuggly onto the faucet making this method for siphoning bathwater a lot easier.